Disposable polymeric articles for packaging, bowls and cups are well known. Such articles are formed of polystyrene, polypropylene, polyethylene terephthalate and the like and may be made by thermoforming, injection molding, injection blow-molding, or other suitable technique. Injection molding has advantages in that a short cycle time is readily achieved, but tends to be more expensive in terms of material and articles so formed tend to have anisotropic properties and therefore exhibit brittleness. Thermoforming likewise tends to have advantageous cycle times, however, the waste generated tends to be excessive. Moreover, the draw which may be imposed on the sheet is limited. U.S. Pat. No. 5,693,278 discloses thermoformed articles produced from polyethylene terephthalate sheet. The excessive waste problem is addressed in the '278 patent by utilizing at least forty percent (40%) by weight recycled material.
U.S. Pat. No. 5,433,337 of Willbrandt discloses an injection A molded drink container to fit in vehicle cup holders. The container has an upper rim with a height of from about {fraction (1/16)} of an inch to about {fraction (1/10)} of an inch and a width of from about 0.15 inches to about 0.25 inches. Note Col. 5 at lines 15-25. U.S. Pat. No. 5,427,269 notes at Col. 5 that this type of container may be produced by an suitable method, but that injection molding is preferred.
As noted hereinabove, injection molding tends to be expensive in terms of material, requiring relatively thick-walled parts to compensate for the anisotropy inherent in the production technique. Disposable containers are preferably made utilizing as little material as possible.
Many consumers are generally reluctant to use conventional disposable drinking cups on a frequent basis due to their “look and feel”, their expense, or their performance. Survey data indicate that consumers in many instances prefer disposable articles whose appearance and performance more closely resemble glassware. Conventional disposable drinking cups produced by blow-molding typically rely upon a relatively prominent curled rim to provide rigidity to the article and accordingly, the article does not resemble glassware to the extent desired. Moreover, even with the prominent top-curl, conventional blow-molded cups typically are not rigid enough to mimic glassware. Injection blow-molding processes and apparatus are widely known and widely used in industry. For example, reference may be had to U.S. Pat. No. 3,183,552 to Farkas, U.S. Pat. No. 3,819,314 to Marcus, U.S. Pat. No. 3,339,231 to Piotrowski and Canadian Pat. No. 995,418 to Cannon et al.
It is known, in general, to use injection blow-molding of polycarbonates to produce an assortment of containers, see Kirk-Othmer Encyclopedia of Chemical Technology, Fourth Edition, Vol. 19, p. 600. Further, U.S. Pat. No. 4,139,517 discloses reusable milk bottles composed of aromatic polycarbonates and is specifically directed to a tinted polycarbonate container to prevent milk spoilage caused by artificial light or sunlight. The patent discloses that the containers can be prepared by well-known techniques, such as extrusion blow-molding, injection blow-molding, rotational molding, thermoforming, injection molding and lamination. No specific processing conditions for the mentioned molding techniques are given.
U.S. Pat. Nos. 4,225,304; 4,230,298; 4,234,302 and 4,308,086, issued to Valyi, disclose a continuous process and apparatus for blow-molding, including injection blow-molding, containers formed of various plastics including polycarbonates. Again, no specific process parameters for producing polycarbonate containers are provided. It is and has been a long standing objective of blow-molding processes to achieve a high productivity, i.e., to develop a process with a rapid, efficient and economical operating cycle.
State of the art processes known heretofore are subject to one or more significant disadvantages. Frequently, they are characterized by a relatively slow operating cycle. A shorter operating cycle is particularly desirable since it is directly translatable into a larger number of end products produced. Processes are known with overlapping cycles in order to reduce overall cycle time, for example, by providing that while one parison is being molded another is being blown and still another is being removed. However, even with processes using overlapping cycles the overall cycle time still leaves much to be desired and still necessitates improvement in cycle time. The foregoing difficulties are further compounded by frequent lack of reliability of prior art processes necessitating frequent interruptions of the operation and thereby further impairing operating efficiency.
U.S. Pat. No. 4,540,543 assigned to Canada Cup, Inc., a subsidiary of Fort James Corporation, discloses an injection blow-molding process and apparatus for hollow plastic articles. The method and apparatus for injection blow-molding hollow plastic articles is characterized by a rapid and efficient operating cycle. The injection mold includes a mold cavity and the blow mold is located adjacent the mold cavity in a side-by-side relationship. The parison is injection molded into the mold cavity onto a core. The parison on the core is separated from the mold cavity by moving the parison on the core axially in a straight path away from the mold cavity, followed by movement in a substantially arcuate path into axial alignment with the blow mold, followed by axial movement in a straight path into the blow mold. The advantage of the method and apparatus of injection blow-molding disclosed in U.S. Pat. No. 4,540,543 compared to previous injection blow-molding methods is in its reliability, preventing interruptions of the injection blow-molding operation and thereby improving efficiency. The method and apparatus as disclosed in U.S. Pat. No. 4,540,543 have been used to manufacture thin walled containers from polystyrene. In particular, disposable containers have been successfully produced from polystyrene. Such polystyrene containers are desirable because they are reusable and have aesthetic clarity. However, for producing permanent ware products which have a nominal thickness typically over 50 mils, it has been found that polystyrene was not acceptable because of breakage. When producing blow-molded permaware containers, it is often useful to incorporate onto the base indicia indicating the origin of manufacture or provide other spatial configurations to the base to aid in subsequent processing steps such as printing or packaging. However, for relatively thick bases, the fluid pressure used in blow-molding is not sufficient to adequately press the parison base against a mold and form an adequately deep molded impression on the base. Previously, such base molding step was accomplished by removing the containers from the continuous blow-molding process and stamping the base of the containers in a wholly separate apparatus. Such separate processing adds significant energy and time costs to the overall process.
Accordingly, an object of the present invention is to provide a reusable permanent ware polycarbonate container prepared by injection blow-molding wherein the container mimics glass but is not as breakable when dropped under normal usage.
Another object of the present invention is to provide a reusable, permanent ware injection blow-molded polycarbonate container that has good clarity but is more durable than other plastic containers such as those formed from polystyrene.
A further object of the present invention is to provide a process for injection blow-molding hollow polycarbonate articles characterized by a rapid, efficient and economical operating cycle.
A still further object of the present invention is to provide a process as aforesaid which is convenient and easy to use on a commercial scale and may be reliably used with high productivity.
Still yet another object of the present invention is to provide a process for injection blow-molding hollow articles characterized by a rapid, efficient and economical operating cycle such as provided by U.S. Pat. No. 4,540,543, but use resins other than polystyrene.
A still further object of this invention is to blow mold hollow permaware containers and mold the base of such containers in a continuous process without having to remove the containers from the blow-molding apparatus.
Other objects and advantages of the present invention will become apparent form the following description and drawings.